Abstract
Purpose: To investigate the feasibility of applying ANOVA newly proposed by Yukinori to verify the setup errors, PTV (Planning Target Volume) margins, DVH for lung cancer with SBRT. Methods: 20 patients receiving SBRT to 50 Gy in 5 fractions with a Varian iX linear acceleration were selected. Each patient was scanned with kV-CBCT before the daily treatment to verify the setup position. Two other error calculation methods raised by Van Herk and Remeijer were also compared to discover the statistical difference in systematic errors (Σ), random errors (σ), PTV margins and DVH. Results: Utilizing two PTV margin calculation formulas (Stroom, Van Herk), PTV calculated by Yukinori method in three directions were (5.89 and 3.95), (5.54 and 3.55), (3.24 and 0.78) mm; Van Herk method were (6.10 and 4.25), (5.73 and 3.83), (3.51 and 1.13) mm; Remeijer method were (6.39 and 4.57), (5.98 and 4.10), (3.69 and 1.33) mm. The volumes of PTV using Yukinori method were significantly smaller (P 0.05) among three methods. Conclusions: In lung SBRT treatment, due to fraction reduction and high level of dose per fraction, ANOVA was able to offset the effect of random factors in systematic errors, reducing the PTV margins and volumes. However, no distinct dose distribution improvement was founded in target volume and organs at risk.
Highlights
Compared to Intensity Modulated Radiation Therapy (IMRT), Stereotactic Body Radiation Therapy (SBRT) is characterized by potent ablative doses and highly conformal dose distributions delivered in a few fractions with a short overall treatment time [1]
Two other error calculation methods raised by Van Herk and Remeijer were compared to discover the statistical difference in systematic errors (Σ), random errors (σ), planning target volume (PTV) margins and DVH
We focused on the verification of variance component analysis raised by Yukinori in Lung Stereotactic Body Radiation Therapy (SBRT) with immobilization devices [10]
Summary
Compared to Intensity Modulated Radiation Therapy (IMRT), Stereotactic Body Radiation Therapy (SBRT) is characterized by potent ablative doses and highly conformal dose distributions delivered in a few fractions with a short overall treatment time [1]. In order to reduce toxicity of normal tissues, the planning target volume (PTV) should be minimized by keeping margins for setup and inter-fractional position errors as low as possible. Calculation of the setup errors and PTV margins plays an important role in Stereotactic Body Radiation Therapy (SBRT), especially in lung tumor treatment. Van Herk et al and Remeijer et al had introduced various methods to calculate systematic and random errors in radiation therapy [5] [6] but the methods should be determined by the categories of radiation therapy, such as IMRT, VMAT, SBRT and SRS. Yukinori [8] et al recently proposed variance component analysis, reducing the effect of random component in systematic errors, especially in hypofractionated radiotherapy, to correct the systematic errors introduced by Remeijer
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